1. Field
An embodiment of the present invention discussed herein relates to a virtual tape system including an actual tape device which stores data on a magnetic tape, and a virtual tape storage device which stores the data, stored in the actual tape device, as a virtual tape volume.
2. Description of the Related Art
A virtual tape system is a system including a virtual tape storage device which stores data stored in an actual tape device as a virtual tape volume. A virtual tape system can control a reading and writing of data at a high speed by the same interface as with a control of a magnetic tape (refer to, for example, Japanese Laid-open Patent Publication No. 2008-077519 and Japanese Laid-open Patent Publication (Translation of PCT Application) No. 2002-520693). Hereafter, a description will be given of a configuration of a heretofore known virtual tape system.
An outline of the virtual tape system is illustrated in FIG. 12.
The virtual tape system 10 is a system which stores data specified by a host computer 11 in an actual tape device 14 and a virtual tape storage device 12. The system includes integrated channel processors (ICPs) 13 connected to the host computer 11, integrated device processors (IDPs) 15 provided between the actual tape device 14 and the ICPs 13, and virtual library processors (VLPs) 16 which execute an overall management.
The ICPs 13, being connected to the host computer 11 via an switch device (not shown), carry out a control of an interface with the host computer 11.
The VLPs 16 execute a control of the whole virtual tape system 10, a management of the volume of the virtual tape storage device 12, and the like.
The IDPs 15 execute a process of backing up, and a process of restoring, the actual tape device 14 with a logical volume of the virtual tape storage device 12.
This kind of virtual tape system 10 employs a redundant configuration by including in advance a plurality of the ICPs 13, a plurality of the VLPs 16, and a plurality of the IDPs 15.
On a write command which is an instruction to write data being issued from the host computer 11, an ICP 13 receives the write command. The ICP 13 recognizes a command category or the like, and executes a control of writing the data into the virtual tape storage device 12.
A VLP 16, based on a result of the process of the ICP 13, executes the management of the volume of the virtual tape storage device 12.
Also, an IDP 15 receives a write command from the VLP 16 and, based on the write command received, executes a control of writing the data into the actual tape device 14.
In the virtual tape system, data which are to be stored are stored in both the actual tape device and virtual tape storage device. Then, a construction is such that, even in the event that one of the devices is inaccessible, or data are lost in one of the devices, a data loss in the whole system is prevented, and a data protection is reliably carried out.
However, in the event that a storing of data is carried out by only the virtual tape storage device due to a failure of the actual tape device, the storing of data is executed by only the virtual tape storage device (a degenerate operation of the virtual tape storage device). This condition continues until the actual tape device is restored but, in the event that a trouble occurs in the virtual tape storage device before the restoration, a data loss occurs.
Also, in the event that an amount of data which are to be stored in the virtual tape storage device exceeds free space of the virtual tape storage device, a write request from the host computer is in a wait status until the actual tape device is restored.
Meanwhile, even in a condition in which both the actual tape device and virtual tape storage device are accessible, in the event that an amount of data based on the write request from the host computer exceeds the free space of the virtual tape storage device, data, among the data stored in the virtual tape storage device, for which fewest access requests are made are deleted from the virtual tape storage device, and a storing of data is carried out using space available due to the deletion (which may be referred to hereafter as a migration process).
The data deleted from the virtual tape storage device by this kind of migration process are stored in the actual tape device. For this reason, in the event that a read request for the data subjected to the migration process is made from the host computer, the data are read from the actual tape device. When reading the data from the actual tape device, a mechanical operation is necessary, such as a tape mounting, or an access to a storage position of the data on a tape. For this reason, it takes more time than in a normal data reading (a reading from the virtual tape storage device).